Nearly 29,000 cautions were handed to criminals by the Metropolitan police in the year to March for offences including robbery, drug-trafficking and rape.

According to figures obtained through a freedom of information request by a Conservative London assembly member, Tony Arbour, the UK's biggest police force issued 28,998 cautions in the period, a quarter of all solved crimes in the capital.

Of these, 5,843 were given out for violent attacks, 165 for sexual offences and five for rape, while 180 offenders were cautioned for grievous bodily harm or wounding, 131 for robbery and 318 for drug-trafficking.

Arbour, who represents South West London in the assembly, said on Monday: "The whole point of the British legal system is that justice should be seen to be done.

"However, a quarter of all solved crimes in London escape punishment.

"The 29,000 cautions and youth warnings given out in private during the last year demonstrate that criminals are getting away with increasingly serious crimes.

"The Crown Prosecution Service is not doing Londoners a service by allowing people who admit their guilt not to go to court.

"It is frustrating for police officers to find that time spent trawling through evidence and catching criminals is ultimately wasted because villains are not brought to justice.

"It is unfair on victims, and the fact that a law-abiding resident will receive the same or even worse punishment for minor traffic offences as drug traffickers, robbers and rapists is simply outrageous."

Police handed out 205,700 cautions in England and Wales in the year to September 2012, according to the latest figures from the Ministry of Justice.

It represented a 12% decrease compared with the previous 12 months, and a 44% fall from the 12 months to September 2007, when the use of cautions peaked at 367,300.

Last month, the policing minister, Damian Green, announced a review of guidelines for issuing police cautions as part of a wider crackdown.

Green said the government's goal was to restrict the use of cautions to ensure that serious criminals would never escape punishment.